Arrangement for a wire section of a paper or board machine

ABSTRACT

A web is formed between two wire loops ( 13, 14 ), in a wire section of a paper or board machine, in connection with which dewatering elements ( 12, 17, 15, 28 ) are placed and in which water is drained from a stock suspension from between the two wires ( 13, 14 ). In the region of a twin-wire zone, a suction roll ( 15 ) is placed within one wire loop and a suction box ( 16 ) having a curved surface is situated in opposed relationship with the suction roll ( 15 ) on the side of the other wire loop. After the suction box ( 16 ), the web is guided, due to the effect of a vacuum of the suction roll ( 15 ), forwards on the surface of the wire loop on the side of the suction roll ( 15 ).

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national stage application of InternationalApp. No. PCT/FI2003/000622, filed on Aug. 26, 2003, the disclosure ofwhich is incorporated by reference herein, and claims priority onFinnish App. No. 20021534, filed Aug. 28, 2002.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The invention relates to an arrangement for a wire section of a paper orboard machine, in which a web is formed between two wire loops, inconnection with which dewatering elements are placed and in which wateris drained from a stock suspension from between said two wires.

In paper or board machines, stock is passed from a headbox to a formingsection, i.e. a wire section, in which water is removed from the stockand a web is formed. In the forming section, or the wire section,different types of formers are used in which water is drained from theweb usually between two wires.

As known in the prior art, in the manufacture of paper and board webs, astock is thus prepared first for the headbox, and fibre material,fillers, and fines and additives are mixed with said stock. The stocksystem mixes the fibres and fillers as well as fines and additives, ifany, to form a stock that is as homogeneous as possible in order to befed to the headbox of a paper or board machine. The headbox spreads thestock suspension produced evenly to the forming section, i.e. the wiresection, where dewatering and the couching of the web begin.

Several different types of wire sections, or formers, in themselvesknown to a person skilled in the art, are known in the prior art:fourdrinier formers, hybrid formers and gap formers. A board machine maycomprise several wire units. In forming sections, water is removed bymeans of forming rolls, suction rolls and by means of blade shoes or theequivalent, which blade shoes typically have several vacuum chambers, sothat the use of vacuum makes pressure pulses more effective. Loadableblades are generally placed on the opposite side of the web to assistdewatering by producing shear forces in the suspension within the web,which shear forces break up fibre flocs, thus improving the forming ofthe web. After that, the fibrous web in formers is generally passed ontoa suction roll, which further removes water from the web, after whichthe web is generally passed to a press section. In connection with thesuction roll, water guide plates or water collecting plates havegenerally been used for recovering the exiting water. This has led toasymmetric dewatering to some extent and it has not been possible toregulate the distribution of dewatering in this arrangement to improveasymmetry.

EP patent 912798 (corresponding FI patent application 965277) disclosesa suction box in a paper machine and a method in a suction box of apaper machine. This document describes a suction box in which a vacuumchamber deck or a set of blades in an equivalent position forms a curvedsupport surface for a wire at least in a running situation. In this kindof suction box, the friction between the wire and the blades or betweenthe wire and the deck is very small. This document describes the use ofa suction box placed on a wire run between two rolls, in whichconnection the suction box enables the run of the wire to be curved, andthe use of the box at a wire guide roll, over which wire guide roll twowires are running, so that the run of the wire on the side of the boxcan be made curved by means of the suction box.

FI patent 106730 discloses an arrangement in the wet end of a papermachine for transferring a web from a forming section to a presssection. The forming section comprises a twin-wire zone defined mutuallyby an upper wire loop and a lower wire loop, after which the web isarranged to follow the upper wire at the point at which the web istransferred from the underside of the upper wire onto the top side of afabric situated in the press section. At the end of the twin-wire zonethere is a suction box within the upper wire loop and, in opposedrelationship with the suction box, an open roll within the lower wireloop, the suction box having a deck which is curved at least in arunning situation such that the tension of the upper wire reduces thenormal force caused by the vacuum of the suction box between the wireand the deck, and which suction box can be provided with a vacuum whichkeeps the web at the suction box mainly apart from the roll and from thelower wire while adhering to the underside of the upper wire andconforming to the curved shape of the deck of the suction box. Membersare arranged in connection with the suction box and/or the roll formaking the web follow the lower wire in a break situation to conduct itto the broke handling system. In the arrangement disclosed here, the webcontinues to travel on the surface of the wire on the side of thesuction box.

SUMMARY OF THE INVENTION

An object of the invention is to eliminate or at least minimize theproblems described above and encountered in the prior art applications.

An object of the invention is to provide a wire section of a paper orboard machine which provides a more uniform distribution of dewateringthan that of the prior-art wire sections.

One object of the invention is also to create a wire section by means ofwhich a higher dry solids content is achieved before a press section,thus making it possible to shorten the wire section. Alternatively, thearrangement in accordance with the invention enables the running speedof the paper machine to be increased in wire section rebuilds.

The arrangement in accordance with the invention makes it possible toreplace the traditionally used, large and expensive suction roll of thewire section with a smaller and less expensive suction roll because theforce acting then on the suction roll is lower than in conventionalarrangements.

In accordance with the invention, a suction box, in which the deck orblades of the suction box can be adjusted to be curved at least in arunning situation or the wire run in the area of the suction box iscurved, is placed in connection with a suction roll, which makes itpossible to control the asymmetry of dewatering and, in addition, ahigher dry solids content is imparted to the web before a press section,so that it is possible to shorten the wire section, when desired,because it is possible, for example, to omit one suction box situated onthe run of the wire since the dewatering capacity increases when thearrangement in accordance with the invention is used.

The invention can be applied in connection with different types offormers, both with vertical and horizontal formers and, advantageously,with hybrid and gap formers.

The invention is applied in the twin-wire zone of the wire section, sothat a suction box having, at least during running, a curved surface isplaced within an upper wire loop at a suction roll situated within alower wire loop. After that, in accordance with the invention, the webis caused to continue its travel on the surface of the lower wire.Advantageously, after the portion covered by the suction box, the rollhas a suction zone in which the web is separated by means of vacuum suchthat the web starts to follow the lower wire. Alternatively, a suctionbox with a curved surface can be situated on the side of the lower wireloop and the roll can be situated on the side of the upper wire loop.

In an advantageous arrangement of the invention, a curved surfacesuction box is placed at a suction roll, which suction roll is providedwith two suction zones, the first of which removes water and the secondof which is arranged in the suction roll after the area covered by thesuction box, the web being separated from the upper wire by means of avacuum produced in the latter suction zone such that the web continuesits travel on the surface of the lower wire loop and does not start tofollow the upper wire.

The suction roll may also comprise only one suction zone, in whichconnection the suction zone is situated at least partly after the curvedsurface suction box in the running direction of the web. In that case,the web is separated from the upper wire by means of the vacuum of thesuction zone of the suction roll such that the web continues its travelon the surface of the lower wire loop.

In the arrangement in accordance with the invention, a curved surfacesuction box is thus placed on the side of the upper wire loop, therebyachieving a better distribution of dewatering because in the prior artapplications the distribution of dewatering of a web has generally beenasymmetric, and the arrangement in accordance with the invention makesit possible to improve the distribution of dewatering because a curvedsurface suction box is placed on the opposite side of the web withrespect to the suction roll, thereby allowing dewatering to be regulatedin both directions. The arrangement in accordance with the inventionthus provides a more uniform distribution of dewatering, so that the webis not formed in an asymmetric manner.

Further, by regulating the dewatering ratio between two curved surfacesuction boxes it is possible to fine tune the two-sidedness of the paperbeing formed (absorption properties, filler distribution).

In accordance with the invention according to an advantageous additionalfeature, a curved surface suction box is also placed in connection witha transfer suction roll which is situated at the end of a wire sectionand by which the web is transferred to a press section, so that by meansof the curved surface suction box placed against the roll, rewetting ofthe web can be prevented and the dry solids content of the web isincreased. By regulating the vacuum levels of both curved surfacesuction boxes it is possible to control the two-sidedness of paper.

In connection with the invention, a low vacuum can be used in thetransfer suction roll and a large, massive suction roll having a highvacuum is not needed as the suction box assists in the transfer of theweb.

In the following, the invention will be described in greater detail withreference to the figures in the appended drawing, but the invention isby no means meant to be narrowly limited to the details of the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one application of the invention in ahorizontal former.

FIG. 2 is a schematic view of another application of the invention in ahorizontal former.

FIG. 3 is a schematic view of one application of the invention in avertical design former.

FIG. 4 is a schematic view of one application of the invention in ahybrid former.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following FIGS. 1-4, the same reference numerals are used ofparts corresponding to one another. FIGS. 1-4 illustrate differentapplications for formers, a horizontal gap former in FIGS. 1 and 2, avertical gap former in FIG. 3 and a horizontal hybrid former in FIG. 4.The principal running direction of the web is denoted with the referencearrow S. A stock suspension is supplied from a slice opening of aheadbox 11 to a former 10, in which in the applications shown in FIGS.1- 3 it first meets a forming roll 12 which forms a gap with a guideroll 22. In the application shown in FIG. 4, the stock is supplied fromthe headbox 11 to a fourdrinier wire section 29 of the former 10 ontothe surface of a lower wire loop 14.

In the applications shown in each of FIGS. 1- 4, the former 10 comprisestwo wire loops 13, 14. The upper wire loop 13 runs while guided byalignment and guide rolls 24. The lower wire loop 14 runs while guidedby alignment and guide rolls 22, 23. In the gap former applicationsshown in FIGS. 1- 3, the forming roll 12 and blade dewatering members 17comprising vacuum chambers for removal of water are placed within theupper wire loop. In FIGS. 3 and 4, blade dewatering members 17comprising vacuum chambers are placed within the upper wire loop 13 andloading blades 28 are placed within the lower wire loop 14 for loadingthe blade in order to produce transverse shear forces and to removewater from the stock suspension.

In FIGS. 1- 4, a suction roll 15 is placed within the lower wire loop 14for removing water from the web. A curved surface vacuum box 16 isplaced within the upper wire loop 13 at the suction roll 15, therebyallowing the two-sidedness of the web to be improved because the vacuumbox 16 is placed on the side of the upper wire loop. In the applicationsshown in FIGS. 1- 4, the suction roll 15 is provided with a transfersuction zone 26, which assures that the web remains on the surface ofthe lower wire loop when the upper wire is separated from the surface ofthe web. In the application shown in FIG. 1, after the suction roll 15the web is passed on the surface of the lower wire loop towards a presssection. The web is transferred from the former 10 to the press sectionby means of a transfer suction roll 18, which is provided with a suctionzone 27 to separate the web on the surface of the lower wire 14. In theapplications shown in FIGS. 1, 2 and 4, the suction roll 15 is providedwith a suction zone 25 for sucking water from the web. In FIGS. 1- 4, apress felt or equivalent of the press section is denoted with thereference numeral 21 and its run is guided by alignment and guide rolls31 (FIG. 1).

In the application shown in FIG. 1, a stock suspension is fed from aheadbox 11 to a gap former 10, in which it first meets a forming roll 12having a dewatering zone 32 in which water is removed from the stocksuspension. After that there are blade dewatering members 17, by meansof which water is removed further from the upper surface of the web.After that, the web is passed over a suction roll 15, a curved surfacesuction box 16 being placed at the suction roll 15 on the other side ofwires 13, 14 within the upper wire loop 13, so that water is removedfrom the web both by means of the suction roll 15 and by means of thesuction box 16. The suction zone 25 of the suction roll 15 extends inthe running direction of the web beyond the area of action of thesuction box 16, whereby it is assured that the web adheres to thesurface of the lower wire 14. The run of the web on the surface of thelower wire loop 14 is ensured by means of a suction box 30. The web ispassed on the surface of the lower wire loop 14 further towards a presssection and to further processing from between a suction roll 18 placedwithin the following belt, felt or wire loop 21 and a curved surfacesuction box 19 placed on the opposite side of the suction roll 18.

In the application shown in FIG. 2, the upper wire loop 13 starts toturn upwards immediately after a suction roll 15, in which connectionthe web is prevented from starting to follow the upper wire 13 by meansof a suction zone 26 of the suction roll 15 and the web is kept on theside of the lower wire loop 14. From here the web is passed downwards onthe surface of the lower wire loop 14 towards a transfer onto thefollowing press felt or equivalent 21, which transfer is accomplished bymeans of a transfer suction roll 18 and a curved surface suction box 19,by which suction box 19 the dry solids of the web is increased and, atthe same time, rewetting of the web is prevented.

FIG.3 shows a vertical former 10 with a forming section placedvertically, and in this application a stock suspension is fed from aheadbox 11 between wire loops 13, 14, and water is removed on a formingroll 12 in a dewatering zone 32, after which there are dewateringelements 17, 28, in which water is removed into vacuum boxes as bladedewatering. After that, the web is passed to a curved surface suctionbox 16 placed at a suction roll 15 between the wire loops 13, 14, wherewater is removed from the web by means of the suction box 16, afterwhich the web is passed on the surface of the lower wire 14 forwards andthe web is separated from the upper wire in a transfer suction zone 26of the suction roll 15. After that there is, in a corresponding manner,a suction roll 18, a curved surface suction box 19 being placed oppositethe suction roll 18 for increasing the dry solids of the web and forpreventing rewetting, and the web is passed to the following processingstep.

FIG. 4 shows a former in which there is first a fourdrinier section 29in which water is removed as blade dewatering 17 and, after the bladedewatering portion where the web runs on the substantially horizontalsurface of the lower wire loop 14, the web is passed to a suction roll15 opposed by a curved surface suction box 16, by means of which,together with the suction roll 15, the asymmetry of dewatering iscontrolled, and the web is passed on the surface of the lower wire loop.The transfer of the web forwards on the surface of the lower wire loopis assured by means of a transfer suction zone 26 of the suction roll15, which transfer suction zone is situated after the curved surfacesuction box 16. The web is transferred to further processing by means ofa suction roll 18 and a curved surface suction box 19, which suction box19 serves to prevent rewetting of the wire at the same time.

Above, the invention has been described with reference to some of itsadvantageous exemplifying embodiments only, but the invention is by nomeans intended to be narrowly limited to the details of saidembodiments.

1-10. (canceled)
 11. A forming section of a paper or board machine,comprising: a first forming wire forming a first wire loop and mountedto travel in a defined running direction, the first wire loop having aweb receiving surface; a second forming wire forming a second wire loopwhich forms a twin-wire zone with the first forming wire, and which ismounted to travel in the defined running direction; a suction rollpositioned within the first wire loop, the suction roll having acylindrical suction surface engaged with the first forming wire, andhaving a suction zone; a suction box having a curved surface positionedwithin the second wire loop and positioned with the curved surface inopposed relationship with the suction roll; and wherein the suction zoneof the suction roll has a portion which extends in the running directionbeyond the suction box so that a web passing between the suction rolland the suction box is guided, due to the effect of the suction zone ofthe suction roll, forwards on the web receiving surface of the firstwire loop.
 12. The forming section of claim 11, wherein the second wireloop is separated from the first forming wire while opposite the suctionroll.
 13. The forming section of claim 11, wherein the suction rollsuction zone is divided into a first suction zone opposite the suctionbox, and a second suction zone which forms the portion which extends inthe running direction beyond the suction box so that a web passingbetween the suction roll and the suction box is guided, due to theeffect of the second suction zone of the suction roll, forward on theweb receiving surface of the first wire loop.
 14. The forming section ofclaim 11, further comprising; a third wire or felt, forming a thirdloop; a second suction roll within the third wire or felt; a secondsuction box having a curved surface positioned within the first wireloop and positioned with the curved surface in opposed relationship withthe second suction roll; and wherein the third suction roll is arrangedto pass a web from the web receiving surface of the first wire loop tothe third wire or felt.
 15. The forming section of claim 14, wherein thesecond suction box is arranged to prevent rewetting of a web as the webpasses from the first wire to the third wire or felt.
 16. The formingsection of claim 11, wherein the first forming wire is positionedbeneath the second forming wire in the twin-wire zone.
 17. A method forforming a paper web in a forming section of a paper or board machine,comprising the steps of: supplying a stock suspension from a headbox toa twin wire former having a first forming wire forming a first wire loopand traveling in a running direction, the first wire loop having a webreceiving surface, and the twin wire former having a second forming wireforming a second wire loop which forms a twin-wire zone with the firstforming wire and travels in the running direction; removing water from aweb formed from the stock suspension through a first side with a suctionroll positioned within the first wire loop, the suction roll having asuction zone engaged with the first forming wire, the water beingremoved by suction of the suction roll through the web receivingsurface; removing water from the web through a second side opposite thesuction roll with a suction box which conforms to a sector of thesuction roll and forms a curved surface positioned within the secondwire loop, the suction box positioned with the curved surface in opposedrelationship with the suction roll; and guiding the web after thesuction box by a portion of the suction zone which extends in therunning direction beyond the suction box so that the web passes betweenthe suction roll and the suction box and is guided, due to the effect ofthe suction zone of the suction roll, forwards on the web receivingsurface of the first wire loop.
 18. The method of claim 17 furthercomprising the step of regulating a dewatering ratio between the suctionroll and the suction box to control the two-sidedness of the paper web.19. The method of claim 17 further comprising the step of separating thesecond wire from the first forming wire while the second wire isopposite the suction roll.
 20. The method of claim 17 wherein thesuction roll suction zone is divided into a first suction zone oppositethe suction box, and a second suction zone which forms the portion whichextends in the running direction beyond the suction box, and wherein thestep of guiding the web is performed with the second suction zone of thesuction roll.
 21. The method of claim 17, further comprising the stepsof: passing the web on to a third wire or felt forming a third loop witha second suction roll positioned within the third loop; and preventingrewetting of the web as the web passes from the first wire to the thirdwire or felt with a second suction box having a curved surfacepositioned within the first wire loop and positioned with the curvedsurface in opposed relationship with the second suction roll.
 22. Themethod of claim 17, further comprising the step of forming the twin-wirezone with the first forming wire positioned beneath the second formingwire.